Abstract:

An X-ray opaque filament is provided, which is constituted of a filament
formed of a thermoplastic resin containing an X-ray opaque agent and has
a dry heat shrinkage of 3.5 to 0% at 130° C. An X-ray opaque
covered filament is provided, which is formed by covering the periphery
of the X-ray opaque filament with a covering fiber. Furthermore, an X-ray
opaque filament is provided, which is constituted of a fiber formed of a
thermoplastic resin containing an X-ray opaque agent and has an oil
containing an ionic surfactant in a ratio of 0 to 10% by mass added
thereto. An X-ray opaque covered filament is provided, which has a
covering fiber formed of a thermoplastic resin having a lower melting
point than the thermoplastic resin constituting the X-ray opaque
filament. A fiber structure is provided which includes the X-ray opaque
filament and/or the X-ray opaque covered filament.

Claims:

1. An X-ray opaque filament formed of a thermoplastic resin containing an
X-ray opaque agent, wherein the X-ray opaque filament has a dry heat
shrinkage of 3.5 to 0% at 130.degree. C.

2. The X-ray opaque filament according to claim 1, wherein the
thermoplastic resin is nylon 12.

3. The X-ray opaque filament according to claim 1, consisting only of the
thermoplastic resin containing the X-ray opaque agent.

4. The X-ray opaque filament according to claim 1, wherein the filament is
a monofilament having a degree of fineness within 1000 to 20000 dtex.

5. The X-ray opaque filament according to claim 1, wherein the filament is
a multifilament having a degree of fineness within 1000 to 20000 dtex and
a degree of fineness per single filament within 20 to 400 dtex.

6. An X-ray opaque filament formed of a thermoplastic resin containing an
X-ray opaque agent, wherein an oil containing an ionic surfactant in a
ratio of 0 to 10% by mass is added.

7. The X-ray opaque filament according to claim 6, wherein the
thermoplastic resin is nylon 12.

8. The X-ray opaque filament according to claim 6, consisting only of the
thermoplastic resin containing the X-ray opaque agent.

9. The X-ray opaque filament according to claim 6, wherein the filament is
a monofilament having a degree of fineness of 1000 to 20000 dtex.

10. The X-ray opaque filament according to claim 6, wherein the filament
is a multifilament having a degree of fineness of 1000 to 20000 dtex and
a degree of fineness per single filament of 20 to 400 dtex.

11. An X-ray opaque covered filament wherein an X-ray opaque filament
formed of a thermoplastic resin containing an X-ray opaque agent is
covered with a covering filament and the X-ray opaque covered filament
has a dry heat shrinkage of 3.5 to 0% at 130.degree. C.

12. The X-ray opaque covered filament according to claim 11, wherein the
X-ray opaque filament is one wherein an oil containing an ionic
surfactant in a ratio of 0 to 10% by mass is added.

13. The X-ray opaque covered filament according to claim 11, wherein the
covering filament has a lower degree of fineness than the X-ray opaque
filament.

14. An X-ray opaque covered filament wherein the X-ray opaque filament
according to claim 1 is used, and the covering filament is at least
partly constituted of a second thermoplastic resin having a lower melting
point than a first thermoplastic resin forming the X-ray opaque filament.

15. The X-ray opaque covered filament according to claim 14, wherein the
melting point of the second thermoplastic resin is 100.degree. C. or more
and lower by 20.degree. C. than the melting point of the first
thermoplastic resin.

16. The X-ray opaque covered filament according to claim 14, wherein the
covering filament is a conjugate filament formed of a core portion and a
sheath portion and the sheath portion of the conjugate filament is formed
of the second thermoplastic resin.

17. A fiber structure comprising the X-ray opaque filament according to
claim 1.

18. An X-ray opaque covered filament wherein the X-ray opaque filament
according to claim 6 is used, and the covering filament is at least
partly constituted of a second thermoplastic resin having a lower melting
point than a first thermoplastic resin forming the X-ray opaque filament.

19. A fiber structure comprising the X-ray opaque filament according to
claim 6.

20. A fiber structure comprising the X-ray opaque filament according to
claim 11.

Description:

TECHNICAL FIELD

[0001]The present invention relates to an X-ray opaque filament, an X-ray
opaque covered filament and a fiber structure using the X-ray opaque
filament and/or the X-ray opaque covered filament. The present invention
particularly relates to an X-ray opaque filament and an X-ray opaque
covered filament each of which is a fiber formed of a thermoplastic resin
containing an X-ray opaque agent, able to be photographed by the use of
X-ray, and suitably used in fabric such as woven fabric, knitted fabric
or nonwoven fabric used in various medical purposes, and relates to a
fiber structure such as woven fabric, knitted fabric and nonwoven fabric
using the X-ray opaque filament and/or X-ray opaque covered filament.

BACKGROUND ART

[0002]It has recently been desired to develop a medical-purpose polymer
material that can be photographed by the use of X-ray. For example,
JP-A-2000-336521 proposes a hollow fiber or hollow monofilament
containing an opaque medium in the hollow portion. This is because, in a
conventional technique known in the art, it was impossible that a powdery
opaque component such as barium sulfate is blended with a polymer
material, melt-spun and drawn. Therefore, JP-A-2000-336521 proposes that
a hollow fiber or hollow monofilament is formed, and thereafter, an
opaque medium is injected into the hollow portion thereof. In addition,
JP-A-2000-336521 describes that the hollow fiber or hollow monofilament
is woven into a braid for use or cut into short fiber pieces for use in
various types of medical members including a bone fixation material such
as pins.

[0003]JP-A-2002-266157 describes the X-ray sensitive fiber formed of a
thermoplastic resin containing an X-ray opaque agent, which cannot be
obtained by melt-spinning and drawing in JP-A-2000-336521. In
JP-A-2002-266157, the X-ray sensitive fiber is used by partly weaving it
into cloth such as surgical gauze.

[0004]Such surgical gauze, if it is left in the body, can be found by
introducing an X-ray opaque filament into part of a fiber constituting
the fabric in advance. However, it is often difficult to find the
surgical gauze left in the body by photograph using X-ray because of the
presence of various organs and body fluid, etc. in the body. Therefore,
the X-ray opaque filament has been desired to have a higher opaque
property than ever.

[0005]However, in the fiber described in JP-A-2000-336521, since an opaque
medium is injected only in the hollow portion of the fiber, the opaque
property is insufficient. Also in the fiber described in
JP-A-2002-266157, since the content of an X-ray opaque agent is not high,
sufficient X-ray opaque performance cannot be obtained. Besides this,
since no consideration is given to post-processability of these two
fibers, when surgical gauze etc., is obtained by applying
post-processing, for example, by weaving a fiber into the gauze, problems
such as wrinkle and loss of the X-ray sensitive fiber alone are raised.

[0006]JP-A-2-118131 proposes a covered X-ray opaque filament, in which a
core filament formed of polypropylene containing an X-ray opaque filler
is covered with a sheath filament having a low degree of fineness than
the core filament. In this fiber, since the core filament is coveted with
the sheath filament, the core filament looks in wavy form. Because of
such specific form, when the fiber is observed under X-ray radiation, not
a straight image but a different image is seen. The fiber can be clearly
distinguished.

[0007]However, also in the covered X-ray opaque filament of JP-A-2-118131,
the X-ray opaque performance thereof is insufficient. In addition, in
JP-A-2-118131, no mention is made of application of the filament and no
consideration is given to post-processability.

DISCLOSURE OF THE INVENTION

Problem to be Solved by the Invention

[0008]The present invention was attained by overcoming the aforementioned
problems. An technical object of the present invention is to provide an
X-ray opaque filament and X-ray opaque covered filament which is
excellent not only in X-ray opaque performance but also in
post-processability and capable of forming a product by weaving it into
woven fabric and nonwoven fabric without occurrence of wrinkle and loss
of a fiber from the product, and further provide a fiber structure which
contains the X-ray opaque filament and/or the X-ray opaque covered
filament.

Means for Solving Problem

[0009]To attain the aforementioned object, the present invention provides
an X-ray opaque filament formed of a thermoplastic resin containing an
X-ray opaque agent, wherein the X-ray opaque filament has a dry heat
shrinkage of 3.5 to 0% at 130° C.

[0010]In another The X-ray opaque filament of the present invention, which
is a filament formed of a thermoplastic resin containing an X-ray opaque
agent, wherein an oil containing an ionic surfactant component in a ratio
of 0 to 10% by mass is added.

[0011]According to the present invention, in the X-ray opaque filament, it
is preferable that the thermoplastic resin is nylon 12.

[0012]According to the present invention, it is preferable that the X-ray
opaque filament consists only of a thermoplastic resin containing an
X-ray opaque agent.

[0013]According to the present invention, it is preferable that the X-ray
opaque filament is a monofilament having a degree of fineness within 1000
to 20000 dtex.

[0014]According to the present invention, it is preferable that the X-ray
opaque filament is a multifilament having a total degree of fineness
within 1000 to 20000 dtex and a degree of fineness per single filament
within 20 to 400 dtex.

[0015]In an X-ray opaque covered filament of the present invention, an
X-ray opaque filament formed of a thermoplastic resin containing an X-ray
opaque agent is covered with covering filament and the X-ray opaque
covered filament has a dry heat shrinkage of 3.5 to 0% at 130° C.

[0016]According to the present invention, in the X-ray opaque covered
filament, it is preferable that the X-ray opaque filament mentioned above
is used.

[0017]According to the present invention, in the X-ray opaque covered
filament, it is preferable that the covering filament has a lower degree
of fineness than the X-ray opaque filament.

[0018]In another X-ray opaque covered filament according to the present
invention, the X-ray opaque filament is used and at least a part of the
covering filament is formed of a second thermoplastic resin having a
lower melting point than a first thermoplastic resin forming the X-ray
opaque filament.

[0019]According to the present invention, in the X-ray opaque covered
filament, it is preferable that the melting point of the second
thermoplastic resin is 100° C. or more and lower by 20° C.
or more than the melting point of the first thermoplastic resin.

[0020]According to the present invention, in the X-ray opaque covered
filament, it is preferable that the covering filament is a conjugate
filament formed of a core portion and a sheath portion, and the sheath
portion of the conjugate filament is formed of the second thermoplastic
resin.

[0021]The fiber structure of the present invention is formed of the X-ray
opaque filament and/or the X-ray opaque covered filament.

EFFECT OF THE INVENTION

[0022]The X-ray opaque filament and X-ray opaque covered filament of the
present invention is formed of a filament containing a thermoplastic
resin containing an X-ray opaque agent and has a dry heat shrinkage of
3.5 to 0% at 130° C. Therefore, when the X-ray opaque filament and
X-ray opaque covered-filament of the present invention are used in
various types of materials such as woven fabric, knitted fabric, nonwoven
fabric, and particularly, medical gauze, occurrence of wrinkle and
deformation of a product, due to large shrinkage, can be prevented and,
at the same time, a high quality product can be obtained.

[0023]Furthermore, the X-ray opaque filament of the present invention can
be twisted. The X-ray opaque filament may be used as the X-ray opaque
covered filament. Moreover, the X-ray opaque filament of the X-ray opaque
covered filament can be twisted. In this way, it is possible that the
X-ray opaque filament is less likely to fall out from a product. In
addition, since the sectional shape of the filament is rendered to be
round, excellent opaque performance is obtained. Therefore, the X-ray
opaque filament and X-ray opaque covered filament can be suitably used in
a medical material such as surgical gauze.

[0024]Furthermore, the X-ray opaque filament and X-ray opaque covered
filament of the present invention are formed of a filament containing a
thermoplastic resin containing an X-ray opaque agent and an oil in which
an ionic surfactant component in a ratio of 0 to 10% by mass is added.
Therefore, when the filaments are shaken in water, foams are less likely
to generate even in the presence of oil. By virtue of this, when products
such as woven fabric, knitted fabric and nonwoven fabric are obtained, a
process for removing spinning oil, for example, washing, is not required.
Furthermore, the filaments can satisfy a foaming test required for
medical gauze. Therefore, the filaments are suitably applied to various
types of medical usages.

[0025]In another type of X-ray covered filament according to the present
invention mentioned above, an X-ray opaque filament formed of a filament
constituting of a first thermoplastic resin containing an X-ray opaque
agent is covered with covering filament and the covering filament is at
least partly formed of a second thermoplastic resin having a lower
melting point than the first thermoplastic resin. When a fiber structure
is formed by partly using the X-ray opaque covered filament and
subjecting the filament to heat processing, at least one portion of the
covering filament covering the X-ray opaque filament can be melted and
solidified to adhere to the filament constituting the fiber structure.
Therefore, it is possible to prevent loss of the X-ray opaque filament
from the fiber structure. In addition, since the sectional shape of the
X-ray opaque filament is not deformed. Accordingly, the fiber structure
excellent in opaque property can be obtained.

[0026]The filament structure of the present invention (products such as
woven fabric, knitted fabric, nonwoven fabric, fiber ball and fiber
laminate) comprises the X-ray opaque filament and/or the X-ray opaque
covered filament of the present invention. Therefore, the fiber structure
can be obtained with the excellent X-ray opaque property while preventing
occurrence of wrinkle and deformation of the product. Furthermore, since
the X-ray opaque filament is less likely to fall out from a product, the
resultant product is excellent in quality and thus suitably applied to
various medical uses.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027]FIG. 1 is a schematic illustration of an apparatus for manufacturing
an X-ray opaque filament according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0028]The present invention will be described more specifically below.

[0029]An X-ray opaque filament and the X-ray opaque filament to be used in
an X-ray opaque covered filament according to the present invention each
are formed of a thermoplastic resin containing an X-ray opaque agent. As
the thermoplastic resin, any thermoplastic resin may be used as long as a
synthetic fiber can be obtained. Examples thereof include a polyamide, a
polyester and a polyolefin. Of them, a polyamide is preferable. Examples
of the polyamide include nylon 6, nylon 66, nylon 69, nylon 46, nylon
610, nylon 12 and polymethaxylene adipamide. The thermoplastic resin may
be a copolymer or a mixture of these components. Of the polyamides, nylon
6 and nylon 12 are particularly preferable.

[0030]The reason why a polyamide is preferable as the thermoplastic resin
is that a polyamide filament has excellent textures such as a soft
texture and a moist texture derived from the feature of a polymer and
such a texture is suitable for medical applications such as surgical
gauze used in contact with an affected area. Furthermore, of the
polyamides, nylon 12 is particularly preferable. This is because nylon
12, in addition to the aforementioned properties, can be melt-spun and
drawn to make filaments even if an X-ray opaque agent is contained in a
large concentration as described later.

[0031]When a polyester is used as the thermoplastic resin, for example,
polyethylene terephthalate, polytrimethylene terephthalate, or
polybutylene terephthalate may be used. When a polyolefin is used, for
example, polypropylene or polyethylene may be used. These components may
be used in the form of a copolymer, a mixture or the like.

[0032]A thermoplastic resin may be used singly or in a mixture of
plurality of types.

[0033]Examples of the X-ray opaque agent to be contained in the
thermoplastic resin include barium sulfate, bismuth subnitrate, tungsten
oxide, thorium oxide and cesium oxide. Of them, barium sulfate is
preferable. This is because it is excellent in X-ray impermeability and
has high thermal resistance and crystal stability. In addition, since
barium sulfate has a small primary particle size and it is possible to
produce particles which are less likely to cause secondary aggregation,
when barium sulfate is kneaded into a thermoplastic resin and melt-spun,
filaments can be obtained with good workability accompanying no increase
of filtration pressure and thread-cut dumpling, etc.

[0034]The particle size of the X-ray opaque agent is preferably large to
some extent in view of improving opaque property. However, particles
having an excessively large size are disadvantageous in view of
dispersing them uniformly into filament. Conversely, particles having an
excessively small size cause a problem of secondary aggregation. In
consideration of the aforementioned points, the size of the primary
particles of the X-ray opaque agent is preferably 0.5 to 10 μm, more
preferably, 0.8 to 8 μm, and particularly preferably, 1.0 to 5 μm.

[0035]The X-ray opaque filament of the present invention is a filament
formed of a thermoplastic resin containing an X-ray opaque agent. To
improve opaque performance, it is preferable that the filament is formed
of a single component, more specifically, formed only of a thermoplastic
resin containing an X-ray opaque agent, in order to increase a resin
portion having the X-ray opaque agent added thereto in the conditions
where degree of fineness is equivalent. More specifically, a sheath/core
conjugate filament containing an X-ray opaque agent only in the core
portion is inferior to the single component filament in opaque property
even if having the same degree of fineness as the single component fiber,
because only the core portion has opaque property.

[0036]When a single component fiber is formed, it is preferable that an
X-ray opaque agent is dispersed almost uniformly in a thermoplastic
resin. To disperse an X-ray opaque agent in a thermoplastic resin almost
uniformly, the X-ray opaque agent and the thermoplastic resin can be
directly kneaded by use of an extruder or the like during a melt-spinning
process. However, preferably, master chip, which contains the X-ray
opaque agent in the large concentration, is prepared in advance, and
then, the master chips are kneaded. This is because the master chips are
kneaded more uniformly.

[0037]The X-ray opaque filament of the present invention can be used
together with another type of filament to form various types of fiber
structures such as woven fabric, knitted fabric, nonwoven fabric, fiber
balls and fiber laminates. Of them, it is preferred to form fabric from
the X-ray opaque filament of the present invention in combination with
another type of filament to constitute, for example, woven fabric,
knitted fabric and nonwoven fabric. The fabric is preferably used as
surgical gauze. When woven or knitted fabric is formed, it is preferable
that the X-ray opaque filament of the present invention is used together
with another type of filament and partly integrated into the texture of
the woven or knitted fabric in a weaving/knitting process. It is also
preferable that after woven or knitted fabric consisting of another type
of filament is produced, the X-ray opaque filament of the present
invention is partly integrated in the texture. When nonwoven fabric is
formed, it is preferable that a web formed of another type of filament is
formed and thereafter, the X-ray opaque filaments of the present
invention are arranged on the web and subjected, for example, to
hydroentanglement processing to form nonwoven fabric.

[0038]When woven fabric or knitted fabric and nonwoven fabric, etc., are
obtained by using the X-ray opaque filament of the present invention in
combination with another type of filament as mentioned above, generally,
a thermal setting process is required in order to improve strength and
integration of the woven fabric, knitted fabric and nonwoven fabric or to
dry them after the hydroentanglement processing. For example, when the
filament of the present invention is used in spun-lace nonwoven fabric,
thermal setting is preferably performed at a heat and dry state at
130° C. Therefore, the dry heat shrinkage under these conditions
is a very important value in the present invention.

[0039]Accordingly, the X-ray opaque filament of the present invention
preferably has a dry heat shrinkage (at 130° C.) of 3.5 to 0%,
more preferably, 2.0 to 0%, further preferably, 1.2 to 0% and still
further preferably, 0.6 to 0%.

[0040]If the dry heat shrinkage is larger than 3.5%, the filament of the
present invention greatly shrinks in a thermal setting process when it is
used together with another type of fiber to form various type of
materials such as woven fabric, knitted fabric and nonwoven fabric, with
the result that a product gets wrinkled and deformed.

[0041]On the other hand, if the dry heat shrinkage is less than 0%, the
filament is extended. Therefore, when the filament of the present
invention is used together with another type of fiber to form, for
example, woven fabric, knitted fabric and nonwoven fabric, the filament
of the present invention gets loose in the product and sometimes falls
out from the product.

[0042]In the present invention, the dry heat shrinkage at 130° C.
is measured as follows. That is, the X-ray opaque filament is rolled up
to 10 rounds by use of a sizing reel of 1 m in length to form a hank,
which is then controlled in moisture at 25° C., 65% RH for 24
hours. Next, a load ( 1/150g) per dtex is applied to the ring of the
hank, and the length (LO) at this time is measured. Furthermore, dry heat
shrinkage treatment is performed under no application of load at
130° C. for 30 minutes, and moisture is controlled at 25°
C. and 65% RH for 24 hours. Subsequently, load ( 1/150g) per dtex is
applied in the same manner as above, the length (L1) at this time is
measured. The numerical values obtained above are fitted to the following
equation to calculate a dry heat shrinkage.

Dry heat shrinkage(130° C.)(%)=[1-(L1/L0)]×100

[0043]To reduce a dry heat shrinkage to 3.5% or less, hot drawing and
relaxation heating treatment are preferably performed as shown
particularly below in the case where the thermoplastic resin is nylon 6,
nylon 12 or polypropylene; however, these treatments differ depending
upon the type of thermoplastic resin. In this manner, the dry heat
shrinkage of 3.5% or less can be attained.

[0044]The X-ray opaque filament of the present invention may be a
monofilament or a multifilament. The X-ray opaque filament may be used as
a long filament or as a short fiber by cutting it. In view of opaque
property alone, a monofilament is preferable. However, when an X-ray
opaque agent is added in a large concentration, a monofilament
deteriorates in flexibility. In the usage requiring flexibility, a
multifilament is preferable.

[0045]When the X-ray opaque filament of the present invention is used in
fabric such as surgical gauze as described later, the X-ray opaque
filament is required to have higher opaque performance. To improve the
opaque performance, it is preferred to increase the content of the X-ray
opaque agent in the filament.

[0046]The larger the content of the X-ray opaque agent in the X-ray opaque
filament, the better in order to improve opaque performance. However,
when the content is excessively large, fiber is broken at spinning or
mechanical properties as a fiber may extremely deteriorate in some cases.
In view of these, the content of the X-ray opaque agent in the filament
is preferably 30 to 85% by mass, more preferably, 40 to 80% by mass,
particularly preferably 60 to 78% by mass, and further preferably, 65 to
75% by mass.

[0047]When nylon 12 is used as a thermoplastic resin, even if a large
amount of X-ray opaque agent is contained in the thermoplastic resin,
melt spinning and drawing can be performed and a filament can be obtained
with good workability.

[0048]The degree of fineness of a single X-ray opaque filament is a factor
influencing opaque property. Therefore, in the case of a monofilament,
the degree of fineness is preferably 1000 to 20000 dtex. In the case of a
multifilament, the degree of fineness of a single filament is set at
preferably 20 to 400 dtex and the degree of fineness of the multifilament
is set at preferably 1000 to 20000 dtex.

[0049]To improve opaque property, either one of a monofilament and a
multifilament (single filaments constituting the multifilament) is
preferably a filament having a substantially circular sectional shape. Of
the substantially circular shapes, a circle close to a complete round
rather than an ellipse is preferable. When the sectional shape is an
ellipse, the distances of some portions through which a beam of X-rays
passes are shorter than those of other portions. In this case, opaque
property may deteriorate. In contrast, when the sectional shape is a
complete circle, the distances of the portions through which a beam of
X-rays passes are equal. As a result, excellent opaque performance can be
obtained.

[0050]In the case of a multifilament, the degree of fineness of a single
filament is low compared to that of a monofilament. When the sectional
shape of the multifilament is substantially circular, the same opaque
performance as that of a monofilament can be obtained. To explain more
specifically, when single filaments are unified to form a dense packing
structure to form a multifilament, the sectional shape of the whole
multifilament becomes virtually circular similarly to the sectional shape
of a monofilament. As a result, the distance of a portion through which a
beam of X-rays passes can be increased, providing good opaque
performance. To keep a multifilament have a virtually circular sectional
shape along with the lengthwise direction, it is preferred to twist the
whole multifilament. The number of twists is preferably 20 T/m or more,
more preferably, 50 T/m or more, and much more preferably, 60 to 120 T/m.

[0051]When the X-ray opaque filament is a multifilament throughout of
which is twisted, integrity of the multifilament can be maintained, with
the result that a single X-ray opaque filament is less likely to fall out
from the product.

[0052]Examples of the X-ray opaque filament of the present invention may
include an X-ray opaque filament having an oil added thereto. The X-ray
opaque filament to which an oil is added has not any difference from
known X-ray opaque filaments in the art. However, the X-ray opaque
filament of the present invention greatly differs in the content of the
added oil from X-ray opaque filaments known in the art. This is an
important feature of the present invention. More specifically, in the oil
added to the X-ray opaque filament of the present invention contains, the
amount of an ionic surfactant component is low.

[0053]The ionic surfactant component refers to a cationic surfactant, an
anionic surfactant and an amphoteric surfactant. Example of the cationic
surfactant may include a quaternary ammonium salt. Examples of the
anionic surfactant include an aliphatic acid salt, organic sulfonate
salt, organic sulfate salt and organic phosphoric acid ester salt.
Examples of the amphoteric surfactant include organic pedine and organic
amine oxide.

[0054]The content of the ionic surfactant in the oil is preferably 0 to
10% by mass, more preferably, 0 to 6% by mass, and particularly
preferably, 0 to 3% by mass. When an oil containing the ionic surfactant
in excess of 10% by mass is added, the resultant X-ray opaque filament
and a product produced from such a filament are likely to bubble when
shaken in water.

[0055]More specifically, in the X-ray opaque filament of the present
invention, the oil to be added contains an ionic surfactant within the
range not exceeding 10% by mass, thereby satisfying the foaming test
described in Appendix 4 of "Manual of Medical Nonwoven Gauze Standard",
the Ministry of Health and Welfare, Notification No. 133 dated Mar. 30,
2000 in Japan. When it is applied to various medical uses, a step of
removing an oil such as a refining step is not required. On the other
hand, the X-ray opaque filament to which an oil containing an ionic
surfactant in excess of 10% by mass is added, fails to satisfy the
aforementioned foaming test due to the surface activity of the ionic
surfactant. Therefore, when such an X-ray opaque filament is applied to
various medical uses, a step of removing an oil such as a refining step
is required.

[0056]Note that the reason that a known oil contains a larger amount of
ionic surfactant than that according the present invention is conceivably
because an antistatic effect is improved by the presence of the ionic
surfactant. In connection with this respect, the content of an ionic
surfactant component is low in the present invention. Therefore, when it
may be concerned that the antistatic effect of the oil is not sufficient,
with the result that the property of unifying filaments during
manufacturing deteriorates, and workability of filaments in transferring
from step to step deteriorates, the antistatic effect of the oil can be
improved by adding a nonionic surfactant. Examples of the nonionic
surfactant include higher alcohols or alkyl phenols. Specific examples
thereof include polyoxyethylene sorbitan fatty acid ester, fatty acid
alkanolamide, polyoxyethylene alkyl ether, and polyoxyethylene
alkylphenyl ether.

[0057]In the present invention, the amount of the oil added to the X-ray
opaque filament is preferably 0.1 to 2.0% by mass based on the mass of
the X-ray opaque filament, more preferably, 0.2 to 1.0% by mass, and
particularly preferably, 0.3 to 0.7% by mass. When the amount of the oil
is less than 0.1% by mass, for example, filaments cannot be sufficiently
unified into a bundle, with the result that it tends to be difficult to
spin filaments. On the other hand, when the content exceeds 2.0% by mass,
for example, a roller may be contaminated with an oil during spinning,
with the result that the operation is tends to be affected.

[0058]The X-ray opaque covered filament of the present invention is formed
by covering an X-ray opaque filament formed of a thermoplastic resin
containing an X-ray opaque agent with a covering filament and has a dry
heat shrinkage of 3.5 to 0% at 130° C.

[0059]The X-ray opaque filament to be used in the X-ray opaque covered
filament preferably has a dry heat shrinkage of 3.5 to 0% at 130°
C. and an oil containing an ionic surfactant component in a ratio of 0 to
10% by mass is preferably added to the filament. The thermoplastic resin
used herein is preferably nylon 12. The X-ray opaque filament is
preferably formed only of a thermoplastic resin containing an X-ray
opaque agent. The X-ray opaque filament to be used in the X-ray opaque
covered filament is preferably a monofilament having a degree of fineness
of 1000 to 20000 dtex, or multifilament having a degree of fineness of 20
to 400 dtex per single filament and a degree of fineness of 1000 to 20000
dtex per whole filament.

[0060]The covering filament to be used in the X-ray opaque covered
filament preferably has a low degree of fineness than the X-ray opaque
filament. The material for the covering filament is not particularly
limited and any one of a natural fiber, a synthetic fiber and others may
be used. Examples of the natural fiber include cotton, hemp and silk
thread. Examples of the synthetic fiber include filaments formed of a
polyamide, polyester and polyolefin.

[0061]The X-ray opaque covered filament, by virtue of the presence of the
covering filament covering the periphery of the X-ray opaque filament,
can be easily entangled with another type of fiber constituting a product
in the form of a fiber structure. Therefore, loss of the X-ray opaque
filament from the product can be prevented. More specifically, loss of
the X-ray opaque filament during not only manufacturing steps for
obtaining a product but also use of the product can be prevented. Thus,
the X-ray opaque covered filament can be used in various products and a
high quality product can be obtained.

[0062]To prevent loss of an X-ray opaque filament from a product as
mentioned above, in the case of a multifilament, the whole multifilament
is preferably twisted, as mentioned above. By virtue of the presence of
the twist in the surface of a multifilament, the multifilament can be
easily entangled with another fiber or filament constituting a product.

[0063]However, in the X-ray opaque covered filament of the present
invention, either a monofilament or a multifilament may be used as the
X-ray opaque filament. However, in either case, the X-ray opaque filament
is preferably covered with a covering filament so as to obtain a
virtually circular sectional shape of the X-ray opaque covered filament.
By virtue of this, even if a multifilament is used, an X-ray opaque
covered filament having a virtually circular sectional shape can be
obtained and provide the same opaque performance as that of a
monofilament having a virtually circular section.

[0064]To obtain such an X-ray opaque covered filament, the covering
filament that covers the X-ray opaque filament preferably has a lower
degree of fineness than the X-ray opaque filament as is described above.
Covering is preformed in the following manner. The X-ray opaque filament
is preferably covered with the covering filament having a number of
twists: 200 to 2000 T/m. The number of twists is preferably 500 T/m or
more, and more preferably, 1000 T/m or more.

[0065]The number of twists of the covering filament and the degree of
fineness of the covering filament per single filament and that of a
unified filament of single filaments can be appropriately selected such
that the sectional shape of a covered X-ray opaque filament is rendered
to be substantially circular.

[0066]In the X-ray opaque covered filament of the present invention, it is
preferable that the X-ray opaque filament itself is twisted. In this
case, the number of twists of the X-ray opaque filament is preferably 2
T/m or more, more preferably, 10 T/m or more, and much more preferably,
20 to 50 T/m.

[0067]By virtue of using such an X-ray opaque filament twisted by itself
is used, the X-ray opaque filament is less likely to fall out from the
X-ray opaque covered filament, meaning that the X-ray opaque filament is
less likely to fall out from a product. Furthermore, when the X-ray
opaque filament is a multifilament, the integrity of a multifilament can
be maintained. Thus, also in this case, a single X-ray opaque filament is
less likely to fall out from the product.

[0068]In the X-ray opaque covered filament of the present invention, the
dry heat shrinkage of the covering filament is not particularly limited.
In contrast, the X-ray opaque covered filament is required to have a dry
heat shrinkage of 3.5 to 0% at 130° C., preferably 2.0 to 0%, more
preferably, 1.2 to 0%, and much more preferably, 0.6 to 0%.

[0069]The dry heat shrinkage of the X-ray opaque covered filament can be
measured in the same manner as in the method of measuring a dry heat
shrinkage of the X-ray opaque filament except that the X-ray opaque
filament is replaced by the X-ray opaque covered filament.

[0070]In the X-ray opaque covered filament of the present invention, it is
preferred to use an X-ray opaque filament to which the aforementioned oil
is added. More preferably, the oil is added to not only the X-ray opaque
filament but also the covering filament. Note that it is also preferable
that the oil is added only to the covering filaments.

[0071]Next, another type of X-ray opaque covered filament of the present
invention as mentioned above will be described in detail.

[0072]The X-ray opaque covered filament employs the X-ray opaque filament
of the present invention. The covering filament thereof is at least
partly formed of a second thermoplastic resin having a lower melting
point than a first thermoplastic resin forming the X-ray opaque filament.

[0073]In this case, it is preferable that the melting point of the second
thermoplastic resin constituting at least part of the covering filament
is 100° C. or more and lower by 20° C. or more than the
melting point of the first thermoplastic resin constituting the X-ray
opaque filament. When the difference between the melting points is less
than 20° C., the X-ray opaque filament itself may be melted
depending upon the heat processing temperature during heat bonding
process for obtaining a fiber structure. In contrast, when the melting
point of the second thermoplastic resin is less than 100° C., the
covering filament is possibly melted when the X-ray opaque covered
filament and a fiber structure such as gauze containing the X-ray opaque
covered filament are sterilized by heating.

[0074]When a fiber structure is formed by using such an X-ray opaque
covered filament as mentioned above and subjected to heat processing, the
second thermoplastic resin constituting the covering filament of the
X-ray opaque covered filament is allowed to melt to adhere to another
type of fiber or filament constituting the fiber structure. By virtue of
this, it is possible to satisfactorily prevent loss of the X-ray opaque
filament from the fiber structure. Since the second thermoplastic resin
of the covering filament has a lower melting point than the first
thermoplastic resin constituting the X-ray opaque filament, it is
possible that only the second thermoplastic resin of the covering
filament melts or softens but the thermoplastic resin constituting the
X-ray opaque filament cannot melt during a heat processing. Therefore, it
is possible to avoid deformation of the sectional shape of the X-ray
opaque filament, with the result that a fiber structure excellent in
opaque property can be obtained.

[0075]The covering filament is at least partly formed of a second
thermoplastic resin; however, it may be a composite filament formed of
the second thermoplastic resin and another type of thermoplastic resin or
a single-component filament formed only of the second thermoplastic
resin. However, it is preferable that at least the surface of the
covering filament is formed of a second thermoplastic resin. Examples of
the second thermoplastic resin include a polyolefin, a nylon-based
copolymer and a polyester based copolymer. To allow the X-ray opaque
filament to adhere tight to another type of fiber or filament
constituting a fiber structure, the second thermoplastic resin preferably
has good adhesion properties with both sides. For example, when the X-ray
opaque filament is formed of nylon 12, a nylon-based copolymer may be
preferably used as the low melting-point thermoplastic resin.

[0076]Examples of the polyolefin that can be used as the second
thermoplastic resin may include polyethylene and polypropylene. In
particular, a low-density polyethylene polymerized in the presence of a
metallocene catalyst is preferable since it has a narrow molecular weight
distribution and high resistance to e.g., thermal decomposition.

[0077]Examples of the nylon-based copolymer that can be used as the second
thermoplastic resin may include a binary copolymer and ternary copolymer
consisting of an arbitrary combination of elements including nylon 6,
nylon 12, nylon 66 and nylon 610 or the like.

[0078]Examples of the polyester-based copolymer that can be used as the
second thermoplastic resin may include a polyester-based copolymer
obtained by copolymerization of a dibasic acid or at least one type of
derivative thereof and at least one type of glycol. Examples of the
dibasic acid that can be used herein include aromatic dibasic acids such
as terephthalic acid, isophthalic acid, phthalic acid, p-oxybenzoic acid,
5-sodium sulfoisophthalic acid, and naphthalene dicarboxylic acid;
aliphatic dibasic acids such as oxalic acid, adipic acid, sebacic acid,
azelaic acid, and dodecane dicarboxylic acid; and alicyclic dibasic acids
such as 1,2-cyclobutanecarboxylic acid. Examples of the glycol include
ethylene glycol, diethylene glycol, triethylene glycol, propanediol,
butanediol, pentanediol, hexanediol, neopentanediol, p-xylene glycol, and
polyalkylene glycol such as polyethylene glycol, polytetramethylene
glycol. Furthermore, a polyester copolymer obtained by copolymerization
of an aromatic polyester and an aliphatic lactone may be preferably used.
Examples of the aromatic polyester include a polymer of an ethylene
terephthalate unit and/or a butylene terephthalate unit, or copolymers
obtained by further copolymerizing isophthalic acid, 2,6-naphthalene
dicarboxylic acid, adpic acid, sebacic acid, ethylene glycol,
1,6-hexanediol or the like to these. As the aliphatic lactone, lactones
having 4 to 11 carbon atoms may be used singly or in combination of two
or more types. Examples of a particularly preferable lactone include
ε-caprolactone and δ-valerolactone.

[0079]When a composite filament is used as the covering filament, a
sheath/core conjugate filament is preferable in which the second
thermoplastic resin as mentioned above is used in the sheath portion and
another type of thermoplastic resin is used in the core portion. When the
sheath/core conjugate filament is used as the covering filament, even if
the sheath portion is melted to adhere to X-ray opaque filament and/or a
filament constituting the fiber structure, the resin of the core portion
is not melted and thereby the strength of the covering fiber can be
maintained. Therefore, when the X-ray opaque filaments are bundled, loss
of a single filament can be effectively prevented.

[0080]Examples of said another type of thermoplastic resin to be used when
a conjugate filament is used as the covering filament include a
polyamide, a polyester and a polyolefin. Examples of the polyamide
include nylon 6, nylon 66, nylon 69, nylon 46, nylon 610, nylon 12 and
polymethaxylene adipamide. Examples of the polyester include polyethylene
terephthalate, polytrimethylene terephthalate, and polybutylene
terephthalate. When a polyolefin is used, polypropylene, polyethylene or
the like may be used. Furthermore, a copolymer or a mixture of these
components may be used.

[0081]When a conjugate filament is used as the covering filament, the
ratio (% by mass) of the second thermoplastic resin to the whole covering
filament is preferably 10% or more, and more preferably, 20% or more.
When the ratio of the second thermoplastic resin is excessively low, the
ratio of the adhesion portion by a heat processing is low, with the
result that X-ray opaque filament is likely to fall out from a fiber
structure.

[0082]The heat processing for melting the second thermoplastic resin
constituting the covering filament may be applied directly to the X-ray
opaque covered filament alone or the X-ray opaque covered filament formed
into a fiber structure such as fabric. In consideration of workability
for forming a fiber structure such as fabric, the heat processing is
preferably applied after the fiber structure is formed.

[0083]As a heat processor for melting the second thermoplastic resin
constituting covering filament of an X-ray opaque covered filament, a
general heat processing apparatus can be used. However, to keep the
sectional shape of the X-ray opaque covered filament, a non-contact type
dry heat processing apparatus such as a slit heater is preferably used.
In this way, an X-ray opaque covered filament, in which at least one
portion of the covering filament is melted to adhere to the X-ray opaque
filament, can be obtained. When the second thermoplastic resin of the
X-ray opaque covered filament is once melted, the resultant X-ray opaque
covered filament is used to form a fiber structure such as woven fabric
or nonwoven fabric, and then, heat processing is applied to the fiber
structure, the second thermoplastic resin once melted and solidified is
further melted again to adhere to the fiber structure. Therefore, loss of
an X-ray opaque filament from the fiber structure can be prevented.

[0084]The fiber structure of the present invention will be described. The
fiber structure of the present invention is constituted of the X-ray
opaque filament and/or the X-ray opaque covered filament of the present
invention, and more specifically, constituted by at least partly using
the X-ray opaque filament and/or the X-ray opaque covered filament of the
present invention. Specific examples of the fiber structure include
fabric such as woven fabric, knitted fabric and nonwoven fabric, a fiber
laminate and a fiber ball. Of them, fabric is preferable and woven and
nonwoven fabric is more preferable. These woven fabric and nonwoven
fabric contain the X-ray opaque filament and/or X-ray opaque covered
filament of the present invention in combination of another type of fiber
constituting the woven and nonwoven fabric. Therefore, the woven fabric
and nonwoven fabric are excellent in opaque property and apparent
quality. In addition, the X-ray opaque filament is less likely to fall
out from the woven and nonwoven fabric.

[0085]When a surgical operation or the like is performed, many pieces of
gauze are used in order to wipe and absorb, for example, blood and body
fluid, of the patient. After the surgery, it is necessary to take out all
pieces of gauze from the patient. However, gauze used in the surgery is
stained red with blood, which is less likely to be distinguished from the
organs of the patient at the incised portion. As a result, gauze is
sometimes left in the body of the patient. When the gauze remains in the
body for a long time, the patient feels physical pain and has fever.
Moreover, the gauze adheres to an organ and likely causes other diseases.
As a measure of preventing such incidents, gauze pieces are counted after
the surgery. However, it is not easy work and takes time to count gauze
pieces stained with blood. In addition, miscount may occur. Hence, this
measure alone may not be sufficient.

[0086]Of the fiber structures of the present invention, fabric such as
woven and nonwoven fabric mentioned above containing a filament having
X-ray opaque property can be detected by using X-ray when the fabric is
left in the body. In this way, all fabric pieces used in the surgery can
be removed. Besides this, according to the present invention, the X-ray
opaque filament having a low dry heat shrinkage is used. Therefore, even
if heat is applied in a heat processing step during fabric manufacturing
process, the resultant product has no wrinkle. The product can be
obtained with good quality and suitably used as medical gauze.
Furthermore, when an X-ray opaque covered filament formed by covering an
X-ray opaque filament with another type of filament (covering filament)
is used, loss of an X-ray opaque filament from the fabric can be
prevented. Moreover, the sectional shape of the resultant filament
becomes substantially circular. Hence, excellent opaque performance can
be obtained.

[0088]As the warp and the weft constituting woven fabric according to the
present invention, any type of fiber such as a synthetic fiber, natural
fiber or regenerated fiber may be used as long as it has fiber form, more
specifically, as long as it has a structure such as a spun yarn formed of
short fibers, a fiber bundle formed of one or more long filaments and a
combination of these. Of these, a natural fiber such as cotton and a
regeneration fiber such as solvent spun cellulose fiber, viscose rayon or
cuprammonium rayon (Cupra rayon) has a relatively good water
absorptivity, and therefore are suitable for wiping and absorbing blood
and body fluid. The fibers constituting the woven fabric may be
constituted of a single type of fiber and two types or more of fibers in
combination as long as the object of the present invention is not lost.

[0089]The warp and weft constituting woven fabric are not particularly
limited by a degree of fineness as long as it is used in plain weave
fabric. For example, a pure cotton yarn such as cotton yarn count 40 may
be used. When the woven fabric is used as medical gauze, the density of
the yarn may fall within the range of those generally used as medical
gauze. However, in view of the absorption amount and handling, both the
ward and waft densities are preferably about 5 to 20 lines/cm.

[0090]The X-ray opaque filament and/or the X-ray opaque covered filament
must be integrated in woven fabric having a flat texture. In weaving
plain weave fabric, the X-ray opaque filament and/or the X-ray opaque
covered filament may be woven as at least one of the warp and or at least
one of the weft or may be inserted after the woven fabric is prepared.

[0091]The woven fabric containing the X-ray opaque filament and/or the
X-ray opaque covered filament thus obtained may be laminated with another
type of woven fabric and/or nonwoven fabric. The laminate can be
subjected to hydroentanglement processing to integrate to each other and
then put in use.

[0092]Next, nonwoven fabric of the fiber structures according to the
present invention will be described.

[0093]The main fiber constituting the nonwoven fabric is preferably a
non-thermoplastic fiber. This is because many thermoplastic fibers are
poor in water absorptivity and thus are not suitable for wiping and
absorbing blood and body fluid. Preferable examples of the
non-thermoplastic fiber include a natural fiber such as cotton, which is
relatively good in water absorptivity, and regeneration fibers such as a
solvent spun cellulose fiber, viscose rayon or cuprammonium rayon (Cupra
rayon). Of them, the solvent spun cellulose fiber is preferable. This is
because it has high crystallinity, high orientation, high initial young
modulus and high strength during wet time. The solvent spun cellulose
fiber is obtained by spinning a raw-material solution in which cellulose
is dissolved in a specific organic solvent without chemically modifying
the cellulose or by spinning chips prepared by drying the raw-material
solution. More specifically, the solvent spun cellulose fiber is sold by
Lenzing under the name/trade name "Lenzing lyocell". The
non-thermoplastic fiber constituting the nonwoven fabric may be
constituted of a single type of fiber or constituted of two types or more
of fibers in combination as long as the object of the present invention
is not damaged.

[0094]A main fiber constituting nonwoven fabric preferably has a degree of
fineness per single fiber of 0.8 to 3.5 dtex and more preferably, 1.0 to
3.0 dtex. If the degree of fineness is less than 0.8 dtex,
transportability of the fiber deteriorates in a carding step of nonwoven
fabric manufacturing process. In contrast, when the degree of fineness
exceeds 3.5 dtex, entangling of mutual fibers becomes poor, with the
result that the degree of entangling at the entangling point decreases.
In addition, the length of fiber is preferably as short as 20 to 85 mm.
When the length of fiber deviates from this range, the transportability
of the fiber deteriorates in a carding step of a nonwoven fabric
manufacturing process.

[0095]The weight per unit area of nonwoven fabric, which is a fiber
structure of the present invention, is preferably 25 to 150 g/m2.
When the weight per unit area is less than 25 g/m2, the absorption
amount of blood or the like is not sufficient. Conversely, when the
weight per unit area exceeds 150 g/m2, the absorption amount
increases; however, it becomes difficult to handle the nonwoven fabric at
the time of surgical operation.

[0096]The X-ray opaque filament and/or X-ray opaque covered filament for
the nonwoven fabric must be contained in an appropriate amount in the
nonwoven fabric. For example, nonwoven fabric according to the present
invention can be formed by forming webs of the main fiber constituting
the nonwoven fabric, arranging the X-ray opaque filaments and/or X-ray
opaque covered filaments between two web layers and subjecting the
resultant construct to hydroentanglement processing. Alternatively,
nonwoven fabric according to the present invention can be obtained by
subjecting a single-layer web to hydroentanglement processing to obtain
nonwoven fabric and arranging the X-ray opaque filament and/or X-ray
opaque covered filament on the surface of the nonwoven fabric obtained
and further subjecting the resultant construct to hydroentanglement
processing.

[0097]When the nonwoven fabric is obtained as described above, generally,
a thermal-setting process must be performed to improve the strength and
integrity of the nonwoven fabric or for dehydration performed, for
example, after hydroentanglement processing. For example, when the
filament of the present invention is used in span-lace nonwoven fabric,
the thermal-setting is performed in a dry and hot state of 130° C.
Therefore, in the present invention, a dry heat shrinkage under such the
conditions is very important value, as described above.

[0098]In a fiber structure according to the present invention having an
X-ray opaque covered filament whose covering filament is formed of a
second thermoplastic resin having a lower melting point than a first
thermoplastic resin constituting the X-ray opaque filament, it is
preferable that the second thermoplastic resin constituting at least part
of the covering filament is melted to adhere to the fiber constituting
the fiber structure.

[0099]As a device for melting the second thermoplastic resin constituting
the covering filament of an X-ray opaque covered filament after the X-ray
opaque covered filament is formed into the fiber structure and contained
therein, a heat processing apparatus may be used. The X-ray opaque
covered filament may be allowed to adhere to the fiber constituting the
fiber structure by a method of melting a second thermoplastic resin by
use of the heat processing apparatus. Examples of the heat processing
method include a method of passing the fiber structure through a
non-contact dry heat processing apparatus such as a slit heater and a
heat press method using a heat roller such as emboss roller. However, in
view of opaque property and flexibility, the non-contact dry heat
processing apparatus is preferably used. In particular, when the melting
point of the second thermoplastic resin constituting the covering
filament is 130° C. or less, the second thermoplastic resin is
melted by thermal-setting performed in a dry state of 130° C.
during a nonwoven fabric manufacturing process. Therefore, the covering
filament is allowed to adhere to the main fiber constituting the nonwoven
fabric during the thermo-setting process.

[0100]A method of manufacturing the X-ray opaque filament (multifilament)
of the present invention will be described.

[0101]As a method of integrating an X-ray opaque agent into a
thermoplastic resin in the present invention, a predetermined amount of
the X-ray opaque agent can be directly added to the thermoplastic resin
in a melt-spinning process and kneaded by an apparatus such as an
extruder. However, there is another method, in which master chips are
previously prepared by adding the X-ray opaque agent to the thermoplastic
resin in a high concentration, and then, the master chips and general
thermoplastic resin chips are blended together and kneaded. This method
is preferable since the X-ray opaque agent can be more uniformly
dispersed.

[0102]To explain more specifically, the master chips containing the X-ray
opaque agent and the thermoplastic resin are kneaded and melted by an
extruder and melt-spun by extruding the molten resin through a spinning
nozzle in accordance with a known method. The spinning temperature is
preferably set within the range of (Tm+10)° C. to (Tm+80)°
C. where Tm is the melting temperature of the thermoplastic resin
containing the X-ray opaque agent. When the spinning temperature is
excessively high, the thermoplastic resin causes thermal decomposition,
rendering smooth spinning difficult; at the same time, the physical
properties of the resultant filament tend to be poor. In contrast, when
the spinning temperature is excessively low, residue such as an unmelted
product is likely to remain.

[0103]The spun filament is cooled and solidified by applying cool air of
15 to 40° C. In this way, the filament is wound once up at a rate
of 200 to 1500 m/minute without being substantially drawn.

[0104]The undrawn multifilament obtained by winding-up as mentioned above
is subjected to heat drawing. In this case, the heat drawing is
preferably performed by applying a drawing tension of 1.0 g/dtex or less
while applying heating processing to the filament at a heat processing
temperature of (Tm-150)° C. to (Tm-50)° C. for a heat
processing time of 0.02 seconds or more.

[0105]When the heat processing time during the drawing is set at 0.02
seconds or more, sufficient calories can be provided. Furthermore, when
the drawing tension is set at 1.0 g/dtex or less, uniform drawing can be
made.

[0106]The heat processing time during the drawing is preferably set at
0.02 seconds or more as mentioned above, more preferably, 0.05 seconds or
more, and further preferably, 0.07 seconds or more. The drawing tension
is preferably set at 1.0 g/dtex or less as mentioned above, more
preferably, 0.8 g/dtex or less, and further more preferably, 0.6 g/dtex
or less.

[0107]The drawing speed is not particularly limited. However, to set the
heat processing time at 0.02 seconds or more, the drawing speed is
preferably set at 500 m/minute or less, and more preferably, 200 m/minute
or less, and further preferably, 100 m/minute or less. In view of the
productivity, the drawing speed is preferably set at 50 m/minute or more.

[0108]The drawing temperature will be described. Generally, drawing is
performed between rollers. When drawing is performed between hot rollers,
the roller temperature is preferably set at (Tm-150)° C. to
(Tm-50)° C. When drawing is performed by setting a heater between
the rollers, the temperature of the heater is preferably set at
(Tm-150)° C. to (Tm-50)° C.

[0109]The heat processing time refers to the total time required for the
multifilament to pass through a heating zone, which is set at within the
temperature range, in a drawing step. More specifically, when preheating
is performed, the time of passing through the preheating zone must be
included.

[0110]The drawing rate is preferably 20 to 60% of a maximum drawing rate
(which is the drawing ratio at which an undrawn multifilament is broken
by drawing). When the drawing ratio deviates from this range, drawing is
not enough or too much.

[0111]Immediately after or in a certain interval after the heat drawing,
relaxation heat processing is preferably performed. The relaxation heat
processing is preferably performed at a tensile stress of 0.5 g/dtex or
less for 0.5 seconds or more within the temperature range of
(Tm-100)° C. to (Tm-30)° C.

[0112]When the relaxation heat processing is performed continuously after
the heat drawing as mentioned above, the multifilament can be
sufficiently drawn and contracted. As a result, the dry heat shrinkage
(at 130° C.) of the X-ray opaque filament of the present invention
can be set at 3.5% or less.

[0113]The X-ray opaque filament (multifilament) of the present invention
can be obtained by the manner as mentioned above or, if necessary, by
twisting it by a known method.

[0114]A method of manufacturing the X-ray opaque covered filament of the
present invention will be described.

[0115]The X-ray opaque covered filament can be obtained by covering the
X-ray opaque filament obtained in the aforementioned manner with a
covering filament. When the X-ray opaque filament is covered with a
covering filament, covering is preferably performed such that the number
of twists of the covering filament is to be 200 to 2000 T/m, more
preferably, 500 to 2000 T/m, and particularly preferably, 1000 to 2000
T/m. When covering is performed, the number of twists of the covering
filament and other conditions may be appropriately selected such that the
cross-sectional shape of the X-ray opaque filament becomes substantially
circular.

[0116]Another type of X-ray opaque covered filament according to the
present invention, which is formed by covering a X-ray opaque filament
with a covering filament that at least partly contains a second
thermoplastic resin having a lower melting point than that of a first
thermoplastic resin constituting the X-ray opaque filament, can be
obtained by covering the X-ray opaque filament with the covering filament
in the manner as mentioned above. The covering filament is obtained by
melt-spinning the second thermoplastic resin in combination with another
type of thermoplastic resin constituting the covering filament by use of
a general composite spinning apparatus such that the covering filament is
obtained, for example, in a sheath/core form, and drawing and heat
processing the resultant filament in accordance with a conventional
method.

[0117]A preferable method of manufacturing an X-ray opaque filament
according to the present invention having an oil added thereto will be
described. In this case, the X-ray opaque filament can be manufactured in
the same manner as mentioned above. The filament obtained by
melt-spinning is cooled and solidified by applying cool air and an oil
may be added in accordance with a known method.

[0118]In the preferable method of manufacturing an X-ray opaque covered
filament according to the present invention having an oil added thereto,
for example, the X-ray opaque filament to which an oil is added as
mentioned above may be used. When X-ray opaque covered filament using a
covering filament having an oil also added thereto is obtained, the
covering filament may be prepared previously in a separate step by adding
an oil thereto by a known method.

[0119]A preferable method for manufacturing woven fabric (plain woven
fabric), which is one of the fiber structures of the present invention,
will be described.

[0120]The woven fabric of the present invention is manufactured using pure
cotton yarn, for example, cotton yarn count 40, as the warp and the weft
by means of, for example, a general gauze weaving machine. In the case
where the X-ray opaque filament and/or the X-ray opaque covered filament
is used in place of at least one of the ward or at least one of the weft,
the X-ray opaque filament and/or the X-ray opaque covered filament may be
integrated into woven fabric and fixed therein. In the case where the
X-ray opaque covered filament, which is formed by covering the X-ray
opaque filament with a covering filament at least partly containing a
second thermoplastic resin having a lower melting temperature than a
first thermoplastic resin constituting the X-ray opaque filament, is
used, the X-ray opaque covered filament can be melted to adhere to cotton
yarn by applying heat processing to the woven fabric obtained.
Furthermore, when heat processing is performed by using a hot emboss
roller or an ultrasonic welding apparatus to melt the X-ray opaque
filament and/or X-ray opaque covered filament to adhere to cotton yarn,
the filament can be fixed more tightly. Alternatively, the X-ray opaque
filaments are arranged on the woven fabric formed of cotton yarn alone
and subjected to heat processing by a hot emboss roller or an ultrasonic
welding apparatus to melt the X-ray opaque filament to adhere to the
cotton yarn. The obtained woven fabric is appropriately defatted,
breached and sterilized to obtain gauze. The obtained gauze can satisfy
the standard defined by the Japanese Pharmacopoeia.

[0121]The X-ray opaque filaments and/or the X-ray opaque covered filaments
are preferably arranged on woven fabric at appropriate intervals in the
machine direction (lengthwise direction) of a manufacturing process of
woven fabric. More specifically, the filaments may be arranged at
intervals of about 10 to 300 mm. The filaments may not only be arranged
linearly but also be arranged in a wavy or zigzag fashion.

[0122]A preferable method of manufacturing nonwoven fabric, which is one
of the fiber structures of the present invention, will be described.

[0123]First, a fiber web is prepared, which is formed by accumulating, for
example, solvent spun cellulose fibers as a main fiber. As the fiber web,
a card web may be used, which is obtained by supplying solvent spun
cellulose fibers to a carding machine. When holes are desired in the
fiber web, a mesh-form support formed of rough woven cloth having
predetermined opening portions, may be used. Subsequently, X-ray opaque
filaments and/or the X-ray opaque covered filaments are arranged at
appropriate intervals on the fiber web. Further on the resultant
structure, a fiber web formed by accumulating solvent spun cellulose
fibers is laminated to obtain a laminate.

[0124]The fiber webs arranged on and under the X-ray opaque filaments
and/or the X-ray opaque covered filaments may be the same or different,
for example, in weight per unit area. The weight per unit area of the
fiber web to be positioned on and under the filaments may be
appropriately selected in consideration of the weight per unit area of
the nonwoven fabric to be finally obtained; however, preferably about 10
to 100 g/m2 each.

[0125]The X-ray opaque filaments and/or the X-ray opaque covered filaments
are preferably arranged on the fiber web at appropriate intervals in the
machine direction (lengthwise direction) of a manufacturing process of a
product. More specifically, the filaments may be arranged at intervals of
about 10 to 300 mm. The filaments may not only be arranged linearly but
also be arranged in a wavy or zigzag fashion.

[0126]To the laminate, which is obtained by laminating a first fiber web,
X-ray opaque filaments and/or X-ray opaque covered filaments, and a
second fiber web in this order, pressurized liquid flow such as
pressurized water flow is applied. In this manner, an entanglement
treatment of, for example, solvent spun cellulose fibers is performed.
Fibers are mutually entangled by application of the pressurized liquid
flow to obtain an entirely integrated fiber sheet. In addition, since
solvent spun cellulose fibers are entangled with X-ray opaque filaments
and/or the X-ray opaque covered filaments, X-ray opaque filaments and/or
the X-ray opaque covered filaments can be fixed to the fiber sheet.

[0127]The pressurized water flow can be obtained by use of a spray
apparatus in which spray nozzles having a pore size of 0.05 to 2.0 mm are
arranged at intervals of 0.05 to 10 mm in a single line or in a plurality
of lines in the direction (transverse direction) perpendicular to the
machine direction of a product manufacturing line. More specifically, the
pressurized water flow can be obtained by spraying water through the
spray nozzles at a pressure of 1.5 to 40 MPa. When the aforementioned
mesh-form support formed of rough woven cloth is used, constituent fibers
move to opening portions of the mesh-form support while being entangled
with each other. However since no fibers are present at the portion
corresponding to the knuckle portions of the support, opening holes are
formed. In this way, nonwoven fabric formed of a fiber sheet having holes
can be obtained.

[0128]The openings of the mesh-form support can be determined depending
upon the surface configuration of the nonwoven fabric to be obtained and
presence or absence of holes. For example, when the mesh-form support is
woven cloth having about 16 to 25 meshes, nonwoven fabric having not only
a smooth surface but also opening holes can be obtained. When the
mesh-form support is woven cloth having 25 meshes or more, opening holes
are less likely to be formed. In particular, when woven cloth has meshes
exceeding 40, the nonwoven fabric obtained has an extremely smooth
surface and excellent in drape property. The size of meshes may be
appropriately selected depending upon the requirements for the nonwoven
fabric to be desired. Note that the term "mesh" refers to the number of
lines per inch. For example, rough woven cloth having 25 meshes refers to
one having 25 lines per inch.

[0129]The nonwoven fabric having the X-ray opaque filaments and/or the
X-ray opaque covered filaments obtained by hydroentanglement processing
is cut into pieces of an appropriate size to obtain the nonwoven fabric
of the present invention, which can be used, for example, as medical
gauze.

[0130]When the X-ray opaque covered filament, in which the periphery of an
X-ray opaque filament is covered with a covering filament at least partly
containing a second thermoplastic resin having a lower melting point than
a first thermoplastic resin constituting the X-ray opaque filament, is
used, the covering filament can be melted to adhere to a main fiber
constituting nonwoven fabric in a thermal setting step carried out for
dehydration after hydroentanglement processing.

EXAMPLES

[0131]The present invention will be now more specifically described by way
of examples below. Note that physical property values are measured and
evaluated in the Examples and Comparative Examples as follows.

(a) Dry Heat Shrinkage (Dry Heat Shrinkage at 130° C.)

[0132]The dry heat shrinkage of the obtained X-ray opaque filament was
measured by the aforementioned method. Note that, in the following
Examples and Comparative Examples, when the degree of fineness of the
obtained X-ray opaque filament was 3800 dtex (28 filaments), the load
(weight to be applied to the ring of a hank) was set at 507 g.

(b) Evaluation of Fiber Structure (Woven Fabric/Nonwoven Fabric)

[0133]The obtained woven fabric and nonwoven fabric were evaluated for
opaque property, wrinkle occurrence and loss of a filament, as follows.

(Opaque Property)

[0134]The obtained woven fabric and nonwoven fabric were photographed by
an X-ray camera under shooting conditions: X-ray irradiation distance: 1
m, X-ray generation apparatus (anode: tungsten) having a tube voltage of
80 kV and a tube current of 400 mA, irradiation time: 0.063 seconds. The
visibility of the X-ray opaque filament and/or the X-ray opaque covered
filament was visually evaluated in accordance with the following 4
grades.

[0135]E: very clearly observed

[0136]G: clearly observed

[0137]M: slightly clearly observed

[0138]P: substantially not observed

(Occurrence of Wrinkle)

[0139]The state of wrinkle appearing in the woven fabric and nonwoven
fabric was visually evaluated in accordance with the following 5 grades.

[0140]1. The fabric is not wrinkled and the quality is good

[0141]2. The fabric is partly wrinkled but the quality is good

[0142]3. The fabric is entirely and slightly wrinkled but the quality is
good

[0143]4. The fabric is entirely and somewhat wrinkled and no practical
problem is observed in quality

[0144]5. The fabric is severely wrinkled and the quality is low.

(Loss of a Filament)

[0145]The obtained woven fabric and nonwoven fabric were cut into pieces.
The X-ray opaque filament and/or the X-ray opaque covered filament (both
multifilament and single filament) were pulled and removed by hand from
the cut edge thereof. The degree of easiness in removing a filament was
evaluated in accordance with the following 4 grades.

[0146]1. When pulled strongly, neither a multifilament nor a single
filament thereof is removed.

[0147]2. Neither a multifilament nor a single filament thereof is removed

[0148]3. Although a multifilament is not removed but a single filament
thereof is removed more or less.

[0149]4. Both a multifilament and a single filament thereof are removed
more or less.

(c) Relative Viscosity

[0150]Nylon 6: Viscosity was measured in accordance with a conventional
method using 96% sulfuric acid as a solvent at a concentration of 1 g/dl
and a temperature of 25° C.

[0151]Nylon 12: Viscosity was measured in accordance with a conventional
method using metacresol as a solvent at a concentration of 0.5 g/dl and a
temperature of 25° C.

[0152]Polyethylene terephthalate: Viscosity was measured using a solvent
mixture containing phenol and tetrachloroethane in equivalent amounts as
a solvent at a sample concentration of 0.5 g/100 cc and a temperature of
20° C., by means of Ubbelohde viscometer.

(d) Foaming Test

[0153]An X-ray opaque filament or X-ray opaque covered filament (10 g) was
washed while stirring in 1.5 L of water of 25° C. for 5 minutes
three times (1.5 L×3) and dried at room temperature. The resultant
filament was placed in a hard glass container having an inner volume of
about 300 mL. To the container, 200 mL of water was accurately added.
After closed tight with a tap, the container was heated in a pressurized
vapor sterilizer at 121° C. for one hour. Thereafter, the hard
glass container was taken out from the pressurized vapor sterilizer and
allowed to stand still until it reached room temperature. The resultant
solution was used as a sample solution. About 5 mL of the sample solution
was taken, placed in a test tube with a tap of 15 mm in inner diameter
and about 200 mm in length, vigorously shaken for 3 minutes and allowed
to stand still. The surface state of the solution was visually observed.
The sample whose foams disappeared in 10 minutes was evaluated as G
(acceptance), whereas the sample whose foams did not disappear in 10
minutes was evaluated as P (rejection).

(e) Amount of Oil Pick Up (OPU)

[0154](i) The mass (A0) of a conical flask dried at 105° C. was
measured.

[0155](ii) 10 g of a test sample (the X-ray opaque filament or the X-ray
opaque covered filament obtained) was taken, placed in the conical flask,
dried by a hot air circulation dryer of 65° C. for 1.5 hours, and
cooled in a desiccator until it reached room temperature. After cool, the
mass (A1) of the conical flask was measured. The mass of the sample was
calculated in accordance with the equation: A1-A0.

[0156](iii) To the conical flask (ii) housing the sample, n-hexane (60 to
70 mL) was added until the sample was sufficiently soaked. The flask was
tapped tight and shaken at 40° C. for 6 minutes to extract an oil.

[0157](iv) The sample was taken out from the conical flask and washed with
15 to 20 mL of n-hexane. Thereafter, the sample was squeezed to remove
n-hexane. N-hexane was collected including n-hexane used in washing and
placed in the conical flask used above.

[0158](v) The conical flask containing n-hexane was soaked in a water bath
of 96 to 100° C. to vaporize/evaporate n-hexane within the conical
flask completely. Thereafter, the conical flask was dried for 2 hours in
a hot air circulation dryer of 105° C. and allowed to cool to room
temperature in a desiccator. After cool, the mass (A2) of the conical
flask was measured and OPU was calculated in accordance with the
following equation.

OPU(%)=(A2-A0)/(A1-A0)×100

(f) Weight of unit area of nonwoven fabric was measured in accordance with
the description of JIS L 1906.

[0159]Chips of nylon 12 (VESTAMIDL 1900, manufactured by Daicel Degussa
Ltd.) having a relative viscosity of 1.90 were prepared so as to contain
60% by mass of barium sulfate in a filament, supplied to a melt extruder,
melted at a spinning temperature of 250° C., extruded from a
spinning nozzle having 28 spinning holes of 0.50 mm in diameter. The
undrawn filament was rolled up at a winding speed of 400 m/minute.

[0160]Subsequently, the obtained undrawn filament was subjected to hot
drawing and relaxation heat processing under hot drawing/relaxation heat
processing conditions shown in Table 1 in accordance with the process
chart shown in FIG. 1. To explain more specifically, as shown in FIG. 1,
an undrawn filament 1 was first pulled by a pulling roller 5 downward
through a guide roller 2 and treated with heat by a box heater 4 provided
below the guide roller 2. At this time, the temperature (heat processing
temperature) of the box heater 4 was set at 150° C. and the heat
processing time was set at 0.09 seconds. Drawing (a draw ratio of 1.2
fold) was performed between the guide roller 2 and the pulling roller 5
while applying a tension (drawing tension) of 0.42 g/dtex to the undrawn
filament. Subsequently, the relaxation heat processing was performed in a
heat processing apparatus 6 having a saddle type plate heater 8 and a
heat roller 9. The relaxation heat processing was performed while
applying a tension of 0.04 g/dtex at a heat processing temperature of
150° C. for a heat processing time of 3.8 seconds. The filament
passed through the heat processing apparatus 6 was wound up to obtain an
X-ray opaque filament of 3800 dtex/28f.

Examples 2 to 5 and 25 to 28, Comparative Examples 1 and 2

[0161]Spinning, drawing, and relaxation heat processing were performed in
the same manner as in Example 1 except that the content of barium sulfate
in a filament was changed to each of the contents shown in Table 1 and
the hot drawing/relaxation heat processing conditions were changed to
obtain the values shown in Table 1, to obtain an X-ray opaque filament of
3800 dtex/28f.

Examples 6-11 and Comparative Examples 3 and 4

[0162]The X-ray opaque filaments obtained in Examples 1 to 5 and
Comparative Examples 1 and 2 and a polyester multifilament formed of
polyethylene terephthalate of 84 dtex/36 f serving as a covering filament
were used. The covering filament was turned around the X-ray opaque
filament by use of a covering twister so as to obtain the number of
S-shaped twist shown in Table 1 to obtain an X-ray opaque covered
filament. Other manufacturing conditions were as shown in Table 1.

Examples 12 and 13 and Comparative Example 5

[0163]Spinning, drawing, and relaxation heat processing were performed in
the same manner as in Example 1 except that the content of barium sulfate
in a filament was changed to each of the contents shown in Table 1 and
the hot drawing/relaxation heat processing conditions were changed to
obtain the values shown in Table 1 to obtain filaments. The filament
obtained was wound up. Subsequently, the filament was twisted by a ring
twister as shown in Table 1 to form an X-ray opaque filament of 3800
dtex/28f.

Examples 14 and 15 and Comparative Example 6 and 7

[0164]Spinning, drawing, and relaxation heat processing were performed in
the same manner as in Example 1 except that the content of barium sulfate
in a filament was changed to each of the contents shown in Table 1 and
the hot drawing/relaxation heat processing conditions were changed to
obtain the values shown in Table 1 to obtain a filament. The filament
obtained was wound up. Subsequently, the filament was twisted by a ring
twister as shown in Table 1 to form an X-ray opaque filament of 3800
dtex/28f.

[0165]Subsequently, an X-ray opaque covered filament was obtained by use
of a covering twister in the same manner as in Example 6.

Examples 16 and 17

[0166]Spinning, drawing, and relaxation heat processing were performed in
the same manner as in Example 3 except that the X-ray opaque agent was
changed to bismuth subnitrate (Example 16) and tungsten oxide (Example
17) and the content of the X-ray opaque agent in a filament to each of
the contents shown in Table 1, to obtain an X-ray opaque filament of 3800
dtex/28f.

[0167]Subsequently, an X-ray opaque covered filament was obtained by a
covering twister in the same manner as in Example 6.

Example 18

[0168]Master chips were prepared using nylon 6 having a relative viscosity
of 2.40 such that the content of barium sulfate in a filament was 55% by
mass, supplied to extruder-type melt spinning machine, melted at a
spinning temperature of 255° C., extruded from a spinning nozzle
having 28 spinning holes of 0.50 mm in diameter. The undrawn filament was
wound up at a winding speed of 400 m/minute.

[0169]Subsequently, the obtained undrawn filament was subjected to hot
drawing/relaxation heat processing machine which was the same as used in
Example 1 and hot drawing and heat processing were performed under the
hot drawing/relaxation heat processing conditions as shown in Table 1 to
obtain an X-ray opaque filament of 3800 dtex/28f.

Example 19 and Comparative Example 8

[0170]Spinning, drawing, and relaxation heat processing were performed in
the same manner as in Example 18 except that the content of barium
sulfate in a filament was changed to each of the contents shown in Table
1 and the hot drawing/relaxation heat processing conditions were changed
to obtain the values shown in Table 1, to obtain an X-ray opaque filament
of 3800 dtex/28f.

Examples 20 and 21 and Comparative Example 9

[0171]Spinning, drawing, and relaxation heat processing were performed in
the same manner as in Example 18 except that the content of barium
sulfate in a filament was changed to each of the contents shown in Table
1 and the hot drawing/relaxation heat processing conditions were changed
to obtain the values shown in Table 1, to obtain an X-ray opaque filament
of 3800 dtex/28f.

[0172]Subsequently, an X-ray opaque covered filament was obtained by a
covering twister in the same manner as in Example 6.

Example 22

[0173]Spinning, drawing, and relaxation heat processing were performed in
the same manner as in Example 18 except that the content of barium
sulfate in a filament was changed to each of the contents shown in Table
1 and the hot drawing/relaxation heat processing conditions were changed
to obtain the values shown in Table 1 to obtain a filament. The filament
obtained was rolled up. Subsequently, the filament was twisted by a ring
twister as shown in Table 1 to form an X-ray opaque filament of 3800
dtex/28f.

Example 23

[0174]Spinning, drawing, and relaxation heat processing were performed in
the same manner as in Example 18 except that the content of barium
sulfate in a filament was changed to each of the contents shown in Table
1 and the hot drawing/relaxation heat processing conditions were changed
to obtain the values shown in Table 1 to obtain a filament. The filament
obtained was wound up. Subsequently, the filament was twisted by a ring
twister as shown in Table 1 to form an X-ray opaque filament of 3800
dtex/28f.

[0175]Subsequently, an X-ray opaque covered filament was obtained by a
covering twister in the same manner as in Example 6.

Example 24

[0176]Master chips were prepared using polypropylene chips (J107G,
manufactured by Mitsui Chemicals Inc.) having a melt flow rate defined in
JIS K7210 of 7 g/10 minutes such that the content of barium sulfate in a
filament was 60% by mass, supplied to extruder-type melt spinning
machine, melted at a spinning temperature of 230° C., extruded
from a spinning nozzle having 28 spinning holes of 0.50 mm in diameter.
The undrawn filament was wound up at a winding speed of 400 m/minute.

[0177]Subsequently, the obtained undrawn filament was subjected to hot
drawing/relaxation heat processing machine which is the same as used in
Example 1 and hot drawing and heat processing were performed under the
hot drawing/relaxation heat processing conditions shown in Table 1 to
obtain an X-ray opaque filament of 3800 dtex/28f.

[0178]Subsequently, an X-ray opaque covered filament was obtained by a
covering twister in the same manner as in Example 6.

Comparative Example 10

[0179]An X-ray opaque covered filament was obtained by a covering twister
in the same manner as in Example 6 except that spinning was performed in
the same manner as in Example 24, undrawn filament wound up was not
drawn, and the number of twists of the covering fiber was changed to that
shown in Table 1.

[0180]Physical property values of the X-ray opaque filaments and X-ray
opaque covered filaments according to Examples 1 to 28 and Comparative
Examples 1 to 10 obtained as mentioned above are shown in Table 1.

[0181]Chips of nylon 12 (ESTAMIDL 1900, manufactured by Daicel Degussa
Ltd.) having a relative viscosity of 1.90 and chips of the same type of
nylon 12 containing barium sulfate in a high concentration were used and
supplied to a melt extruder such that the content of barium sulfate in
the whole chips was 60% by mass, melted at a temperature of 250°
C., extruded from a spinning nozzle having 28 spinning holes of 0.50 mm
in diameter. To the resultant filament, an oil having a composition (% by
mass) shown in Table 2 was added. The filament was wound up at a winding
speed of 400 m/minute to obtain an undrawn filament.

[0182]Subsequently, the obtained undrawn filament was subjected to the hot
drawing and relaxation heat processing in accordance with the steps shown
in FIG. 1 in the same manner as in Example 1 under the hot
drawing/relaxation heat processing conditions shown in Table 2. The
filament to which hot drawing and relaxation heat processing were applied
was rolled up from the out port of the heat processing apparatus 6 to
obtain X-ray opaque filament (not twisted), which is a multifilament of
3800 dtex/28f.

[0183]Subsequently, the solvent spun cellulose fibers (degree of fineness
per single filament: 1.7 dtex, fiber length: 38 mm, brand name/trade
name: "Lenzing lyocell" manufactured by Lenzing) was opened in a random
carding machine to obtain a fiber web of about 15 g/m2. The X-ray
opaque filaments obtained above were arranged linearly on the fiber web
in the machine direction (lengthwise direction) at intervals of 100 mm.
Further on the filaments, the same web of about 15 g/m2 obtained in
the above was laminated to obtain a laminate.

[0184]The obtained laminate was placed on a mesh-form support having 100
meshes and treated twice by a spray apparatus in which spray nozzles
having a pore size of 0.1 mm were arranged transversely in a single line
at intervals of 0.6 mm at a spray pressure of 6.9 MPa. Subsequently, the
laminate was turned upside down and the rear surface was treated by the
spray apparatus twice at a spray pressure of 9.8 MPa. The laminate was
further turned upside down and placed on a mesh-form support having 25
meshes and treated by the spray apparatus twice at a spray pressure of
9.8 MPa to obtain nonwoven fabric having a weight per unit area of 33
g/m2.

Examples 30 and 31 and Comparative Examples 11 to 14

[0185]An X-ray opaque filament was obtained in the same manner as in
Example 29 except that the composition of an oil, the content of barium
sulfate and hot drawing/relaxation heat processing conditions were
changed to obtain the values shown in Table 2. Note that, in Comparative
Examples 13 and 14, a covering filament was turned around the obtained
X-ray opaque filament so as to obtain the number of S-shaped twists shown
in Table 2 by use of a covering twister to obtain an X-ray opaque covered
filament.

[0186]Subsequently, nonwoven fabric was obtained in the same manner as in
Example 29 by using the X-ray opaque filament obtained.

Example 32

[0187]An X-ray opaque covered filament was obtained using the X-ray opaque
filament obtained in Example 31 and using polyester multifilament of 84
dtex/36f formed of polyethylene terephthalate and having the oil having
the composition shown in the column "Example 32" of Table 2 added
thereto, as the covering filament, more specifically, by turning the
covering filament around the X-ray opaque filament so as to obtain the
number of S-shaped twists of 500 T/m.

[0188]Subsequently, nonwoven fabric was obtained in the same manner as in
Example 29 using the X-ray opaque covered filament obtained.

[0190]As is apparent from Table 2, in Examples 29 to 32, since the content
of an ionic surfactant in the oil added thereof was 10% or less, foams
disappeared within 10 minutes in a foaming test for the X-ray opaque
filament and X-ray opaque covered filament. These filaments satisfied the
object of the present invention. The nonwoven fabric obtained had neither
wrinkle nor loss of a filament and good opaque property.

[0191]On the other hand, in the X-ray opaque filaments of Comparative
Examples 11 to 14, since the content of an ionic surfactant in the oil
added thereto exceeded 10%, foams did not disappear within 10 minutes in
the foaming test. The nonwoven fabric obtained has many wrinkles and the
quality in view of a product was low.

[Examples and Comparative Examples of Woven Fabric]

Example 33

[0192]Woven fabric (plain woven fabric) of 30 cm in width was obtained by
using cotton yarn of yarn count 40 as the warp and weft such that 12
warps and wefts were contained per cm2. On the woven fabric, the
single X-ray opaque filament obtained in Example 5 was placed in parallel
to the warp. The resultant construct was subjected to heat processing
applied by an embossing apparatus to weld the X-ray opaque filament to
the woven fabric to fix it.

[0193]Note that the embossing apparatus has a bumpy roll having scattered
projections, which occupied a ratio of 15% to the whole area of the roll
and were heated to a temperature of 235° C.

Example 34

[0194]Woven fabric (plain woven fabric) was obtained in the same manner as
in Example 33 except that one of the warps was replaced with the X-ray
opaque filament obtained in Example 4 in place of placing a single X-ray
opaque filament on the fabric and bonding it by heat processing to fix
it.

Example 35

[0195]Woven fabric (plain woven fabric) was obtained in the same manner as
in Example 33 except that one of the warps was replaced with the X-ray
opaque filament obtained in Example 3 in place of placing a single X-ray
opaque filament on the fabric and bonding it by heat processing to fix
it. The woven fabric was subjected to heat processing applied by an
embossing apparatus to bond the X-ray opaque filament to the woven fabric
to fix it in the same manner as in Example 33.

Examples 36 to 60 and Comparative Examples 15 to 24

[0196]Woven fabric (plain woven fabric) was obtained in the same manner as
in Example 34 except that one of the warps was replaced with the X-ray
opaque filament or the X-ray opaque covered filament (obtained in each of
Examples) shown in Table 3.

[0197]The physical property values and evaluations of woven fabric samples
of Examples 33 to 60 and Comparative Examples 15 to 24 obtained as
described above are shown in Table 3.

[0198]As is apparent from Table 3, in the X-ray opaque filaments or X-ray
opaque covered filaments according to Examples 33 to 60, since the dry
heat shrinkage of each of the filaments was 3.5% or less, the woven
fabric samples obtained by using the filaments had neither wrinkle
occurrence nor loss of a filament and satisfactory opaque property. In
particular, the X-ray opaque covered filaments of Examples 42 to 47, 50
to 53, 56, 57, 59 and 60 had less loss of the X-ray opaque filaments
since the X-ray opaque filaments were covered. In addition, since the
X-ray opaque covered filaments were integrally formed such that the
sectional shape of a multifilament is substantially circular, the woven
fabric samples obtained by using these filaments had more excellent X-ray
opaque property.

[0199]On the other hand, in each of the X-ray opaque filaments or X-ray
opaque covered filaments according to Comparative Examples 15 to 24,
since the dry heat shrinkage (at 130° C.) of the X-ray opaque
filament exceeded 3.5%, the woven fabric samples obtained by using these
had many wrinkles and the quality in view of a product was low.

[Examples and Comparative Examples of Nonwoven Fabric]

Example 61

[0200]Solvent spun cellulose fiber A (degree of fineness per single
filament: 1.7 dtex, fiber length: 38 mm, brand name/trade name: "Lenzing
lyocell" manufactured by Lenzing) was opened in a random card to obtain a
fiber web of about 15 g/m2. The X-ray opaque filaments obtained in
Example 5 were arranged linearly on the fiber web at intervals of 100 mm
in the machine direction (lengthwise direction). Further on the
filaments, the same web of about 15 g/m2 obtained in the above was
laminated to obtain a laminate.

[0201]The obtained laminate was placed on a mesh-form support having 100
meshes and treated twice by a spray apparatus in which spray nozzles
having a pore size of 0.1 mm were arranged transversely in a single line
at intervals of 0.6 mm at a spray pressure of 6.9 MPa. Subsequently, the
laminate was turned upside down and the rear surface was treated by spray
twice at a spray pressure of 9.8 MPa. The laminate was further turned
upside down and placed on the mesh-form support having 25 meshes and
treated by the spray apparatus twice at a spray pressure of 9.8 MPa. As a
result, nonwoven fabric having a weight per unit area of 33 g/m2.

Examples 62 to 69, 74 to 92 and Comparative Examples 25 to 34

[0202]Nonwoven fabric (weight per unit area: 33 g/m2) was obtained in
the same manner as in Example 61 except that the X-ray opaque filament
was changed to the X-ray opaque filament or the X-ray opaque covered
filament (each of Examples and Comparative Examples) shown in Table 4.

Examples 70 and 71

[0203]Nonwoven fabric was obtained in the same manner as in Example 62
except that the weight per unit area of the nonwoven fabric was changed
to each of the values shown in Table 4.

[0206]As is apparent from Table 4, in the X-ray opaque filaments or X-ray
opaque covered filaments according to Examples 61 to 92, since the dry
heat shrinkage of each of the filaments was 3.5% or less, the nonwoven
fabric samples obtained had neither wrinkles nor loss of a filament and
satisfactory in opaque property. In particular, the X-ray opaque covered
filament of each of Examples 74 to 79, 82 to 85, 88, 89, 91 and 92 had
little loss of the X-ray opaque filaments since the X-ray opaque
filaments were covered. In addition, since the X-ray opaque covered
filament were integrally formed such that the sectional shape of a
multifilament was substantially circular, the nonwoven cloth samples
obtained by using these filaments had more excellent X-ray opaque
property.

[0207]On the other hand, in each of the X-ray opaque filaments or X-ray
opaque covered filaments according to Comparative Examples 25 to 34,
since the dry heat shrinkage (at 130° C.) of the X-ray opaque
filament exceeded 3.5%, the nonwoven fabric samples obtained by using
these had many wrinkles and the quality in view of a product was low.

[Examples of an X-Ray Opaque Covered Filament Whose Covering Filament is
at Least Partly Formed of a Second Thermoplastic Resin Having a Lower
Melting Point than a First Thermoplastic Resin Used in an X-Ray Opaque
Filament]

(Covering Filament a)

[0208]Chips of a nylon copolymer (melting point: 118° C.,
manufactured by Arkema) consisting of nylon 6, nylon 66 and nylon 12 in a
component ratio (by mass) of 42:18:40 were supplied to extruder-type melt
spinning machine and spun and extruded from a spinning nozzle having 12
spinning holes of 0.35 mm in diameter at a spinning temperature of
185° C. Drawing was performed by setting first and second roller
speeds at 560 m/minute and a final rolling-up speed at 1400 m/minute, so
as to obtain a drawing rate of 2.5 fold. The obtained covering filament a
had a degree of fineness of 110 dtex/12f as is shown in Table 5.

(Covering Filament b)

[0209]Nylon 12 (VESTAMIDL 1900, melting point: 178° C.,
manufactured by Daicel Degussa Ltd.) having a relative viscosity of 1.90
was employed as a core component, and a nylon copolymer (melting point:
118° C., manufactured by Arkema) consisting of nylon 6, nylon 66
and nylon 12 in a component ratio (by mass) of 42:18:40 was employed as a
sheath component. A composite covering filament containing the core
component and the sheath component in a mass ratio of 90:10 was spun and
extruded from a core/sheath type composite spinning nozzle having 12
spinning holes of 0.35 mm in diameter at a spinning temperature of
250° C. The filament was rolled up by setting a first roller speed
at 3000 m/minute, a second roller speed at 3200 m/minute, and a final
rolling-up speed at 3500 m/minute. The obtained covering filament had a
degree of fineness of 90 dtex/24f, as is shown in Table 5.

(Covering Filaments c and d)

[0210]Covering filaments were obtained by melt-spinning in the same manner
as in the case of covering filament b except that each of the core to
sheath mixing ratio was set at the value shown in Table 5. The results
are shown in Table 5.

(Covering Filament e)

[0211]Polyethylene terephthalate having a relative viscosity of 0.70 was
employed as a core component, and a copolymer of polyethylene
terephthalate (melting point: 135° C.) having a relative viscosity
of 0.68 and isophthalic acid (33.0% by mole) was employed as a sheath
component. A conjugate covering filament containing the core component
and the sheath component in a mass ratio of 50:50 was spun and extruded
from a sheath/core type conjugate spinning nozzle having 24 spinning
holes of 0.2 mm in diameter at a spinning temperature of 280° C.
The filament was wound up by setting a first godet roller speed at 3000
m/minute (roller temperature: 90° C.), a second godet roller speed
at 4500 m/minute (roller temperature: 110° C.) and a winding up
speed at 4500 m/minute. The obtained covering filament had a degree of
fineness of 84 dtex/24f, as is shown in Table 5.

(Covering Filament f)

[0212]Polyethylene terephthalate (melting point: 260° C.) having a
relative viscosity of 0.70 was employed as a core component, and
polyethylene (melting point: 102° C., melt-flow rate: 20 g/10
minutes) polymerized in the presence of a metallocene based catalyst was
employed as a sheath component. A conjugate covering filament containing
the core component and the sheath component in a mass ratio 50:50 was
spun and extruded from a core/sheath type composite spinning nozzle
having 24 spinning holes of 0.2 mm in diameter at a spinning temperature
of 280° C. and wound up at a winding up speed at 4000 m/minute.
The obtained covering filament had a degree of fineness of 84 dtex/24f as
is shown in Table 5.

(Covering Filament g)

[0213]Nylon 12 (melting point: 178° C.) having a relative viscosity
of 1.90 used in the case of covering filament b was spun and extruded
from 24 spinning holes of 0.35 mm in diameter at a spinning temperature
of 250° C. The obtained filament was drawn by setting first and
second roller speeds at 560 m/minute and a final winding up speed at 1400
m/minute so as to obtain a drawing ratio of 2.5 fold. The obtained
covering filament had a degree of fineness of 90 dtex/24f, as is shown in
Table 5.

(Covering Filament h)

[0214]Polyethylene terephthalate (melting point: 260° C.) having a
relative viscosity of 0.70 was spun and extruded from 36 spinning holes
of 0.2 mm in diameter at a spinning temperature of 280° C. The
obtained filament was wound up by setting a first godet roller speed at
3000 m/minute (roller temperature: 95° C.), a second godet roller
speed at 4500 m/minute (roller temperature: 130° C.) and a winding
up speed at 4500 m/minute. The obtained covering filament had a degree of
fineness of 84 dtex/36f, as is shown in Table 5.

[0215]The covering filament c was turned around the X-ray opaque filament
of Example 5 by use of a covering twister so as to obtain the number of
S-shaped twists: 500 T/m to obtain an X-ray opaque covered filament.

Examples 94 to 103

[0216]An X-ray opaque covered filament was obtained by covering an X-ray
opaque filament with a covering filament in accordance with the
conditions shown in Table 6 (as to combinations of X-ray opaque filament
of Examples and covering filaments and conditions). Note that, in
Examples 96 and 97, X-ray opaque filaments before forming into X-ray
opaque covered filaments in Examples 16 and 24, respectively were used.
In Example 95, after an X-ray opaque filament was covered with a covering
filament, a heating process was performed by use of a slit type heater
heated to 130° C. for 30 seconds to melt part of the covering
filament and solidify it. In this way, the X-ray opaque filament and the
covering filament were bonded with heat.

[0217]A fiber web was obtained in the same manner as in Example 61 using
solvent spun cellulose fiber A used in Example 61 as a main fiber for
constituting nonwoven fabric. Subsequently, on the fiber web, the X-ray
opaque covered filaments of Example 93 were arranged linearly at
intervals of 100 mm in the machine direction (lengthwise direction).
Further on the resultant structure, the same fiber web obtained above was
laminated to obtain a laminate.

[0218]High pressure water spray treatment was applied to the obtained
laminate in the same manner as in Example 61. The fiber sheet obtained by
the spray treatment was allowed to pass through a non-contact dry heat
processing apparatus. In this manner, thermosetting was performed at
130° C. for 30 seconds; at the same time, part of the covering
filament was melted to adhere to the main fiber constituting the nonwoven
fabric to obtain nonwoven fabric having a weight per unit area of 33
g/m2. The physical properties of the nonwoven fabric are shown in
Table 7.

Examples 105 to 109, 112 to 114

[0219]Nonwoven fabric was obtained in the same manner as in Example 104
except that the type of X-ray opaque covered filament and weight per unit
area thereof and the temperature of the thermosetting process were
changed to obtain the values shown in Table 7. The physical properties of
the obtained nonwoven fabric are shown in Table 7.

Examples 110 and 111

[0220]As a main fiber constituting nonwoven fabric, cotton C of Example 73
(Example 100) and viscose rayon fiber B of Example 72 (Example 101) were
used. Nonwoven fabric was obtained in the same manner as in example 104
except that types of X-ray opaque covered filaments were changed as shown
in Table 7. The physical properties of the obtained nonwoven fabric are
shown in Table 7.

[0221]The nonwoven fabric samples obtained in Examples 104 to 114 were not
wrinkled and had good quality and excellent in X-ray opaque property.
Furthermore, since the covering filament is partly melted to adhere to
the X-ray opaque filament and the main fiber constituting nonwoven fabric
in each of Examples 104 to 112, the X-ray opaque filament is not pulled
out from the nonwoven fabric. Therefore, the evaluation as to loss of an
X-ray opaque filament from nonwoven fabric was particularly good.